A midpoint of an individual light source can be defined for example geometrically as an area centroid of a light exit surface of the individual light source. Alternatively, a midpoint of an individual light source can also be defined optically as that point in a light exit surface of the individual light source at which a luminance of the emitted light radiation has a maximum. In the context of the present invention, an extent of an individual light source in a predefined axial direction is generally defined as an extent of a light exit surface of the individual light source in the predefined axial direction through a midpoint of the individual light source, the midpoint being defined as above, for example. In particular, the first extent L1 of the first individual light source is defined as the extent of a light exit surface of the first individual light source in the direction of the first axial direction A1 through the midpoint M1 of the first individual light source.
In the course of the use of an optical viewing apparatus, for example of a surgical microscope, different illumination requirements may occur during operation.
In ophthalmo-cataract surgery, for example, it may be necessary to be able to change very rapidly a plurality of properties of the illumination device, such as, for example, the size of the illumination spots, the illumination angles and/or the brightness of the illumination depending on the respective operation situation. The combination of a plurality of properties of an illumination device constitutes a particular challenge under the confined space conditions of a surgical microscope.
Limits are imposed on the miniaturization of illumination devices which emit high light powers. The light emission of a light source is dependent on its light-emitting surface. Mechanical or electrical aspects, such as mechanical mounting or current supply, additionally have to be taken into account when light sources are combined. Thermal properties also limit miniaturization.